Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Qual é a média de voltas na grade 15?
 ###Tabelas: CREATE TABLE participation_and_medals (participation_and_medals_id AUTO_INCREMENT PRIMARY KEY, Games INT, First INT, Last INT, Gold INT, Silver INT, Bronze INT, Total INT, Best finish (first/last) VARCHAR) CREATE TABLE defunct (defunct_id AUTO_INCREMENT PRIMARY KEY, Venue VARCHAR, Location VARCHAR, Environment VARCHAR, Closed VARCHAR, Reason VARCHAR) CREATE TABLE 125cc_classification (125cc_classification_id AUTO_INCREMENT PRIMARY KEY, Rider VARCHAR, Manufacturer VARCHAR, Laps INT, Time VARCHAR, Grid INT) CREATE TABLE list_of_blood_agents (list_of_blood_agents_id AUTO_INCREMENT PRIMARY KEY, Agent VARCHAR, Melting / boiling point VARCHAR, Effectiveness as blood agent INT, Persistence, open area INT, Persistence, enclosed area INT, Field stability INT, Storage stability INT, Toxicity as blood agent INT) CREATE TABLE 75_million_to_79_million_records (75_million_to_79_million_records_id AUTO_INCREMENT PRIMARY KEY, Artist VARCHAR, Country of origin VARCHAR, Period active VARCHAR, Release-year of first charted record INT, Genre VARCHAR, Claimed sales VARCHAR)  
SELECT AVG Laps FROM 125cc_classification WHERE Grid = 15